Abrasive tool



June 19, 1934. o. s. BUCKNER ABRAS IVE TOOL Original Filed May 51, 1927zyi Z ji lve q Patented June 9, 1934 UITED STATES 195,383. Divided andthis application July 16,

1931, Serial No. 551,133

Claims.

This application is a division of my application filed May 31, 1927,Serial Number 195,383, for Abrasive tools and processes of making thesame and relates to the abrasive tools made by the 5 processes disclosedtherein.

Abrasive or attrition materials, such as corundum, emery, artificialcorundum, crystalline alumina, carbide of silicon and other well knownforms of granular abrasives, are usually composed of irregularly shapedgrains, except in the case of certain crystalline forms which are ofregular formation. That is, so far as I am aware, all forms of abrasivegrains are unequi-dimensional, and while most granular abrasives containa substantial proportion which are distinctly elongated, the largeproportion of elongated grains is usually particularly apparent wherethe grains are of the larger sizes, such as are generally employed inthe construction of abrasive tools which are to be used for rough work,such as cleaning castings, or where a heavy chip is to be removed.Abrasive grains of elongated formation necessarily have correspondinglyflattened sides, which are much less effective, when engaged with thework, than the ends thereof, even though the ends may not be sharplypointed or knife edged.

In the construction of abrasive tools such as blocks, wheels, cylinders,etc., it is customary to mix abrasive material with various forms oforganic or ceramic bonds which are adapted to be softened or fused whensubjected to heat, then to place the mixture in a mold of the shapedesired and subject the mass to considerable pressure, so that it iscompressed into a cake, which is then baked, causing the bond to becomesoftened or fused, so that, when it hardens, on cooling, the grains willbe firmly bound together.

In performing this process, the grains of abrasive have been fixed inthe bond in practically the positions in which they chance to fall, whenplaced in the mold, so that, while some of the elongated grains arelikely to lie in approximately perpendicular relation to thework'engaging face of the tool, much the greater proportion thereof arelikely to lie with their sides either in parallel relation to the face,or at various angles between parallel and perpendicular positionsrelative thereto. As this condition obtains throughout the mass, itfollows that it is indicative of the condition of the work engaging faceat any time.

The degree to which an abrasive article is free cutting depends to alarge extent on the sharpness of the abrading or cutting surface, and,as it is usually desired that an abrading tool be as free cutting aspossible, any condition which increases the sharpness of the cuttingsurface without detrimental effect otherwise increases its efliciency.If the elongated grains of abrasive lie mainly flatwise to the surface,it follows that the sharpness of the surface will be decreased bycomparison with a condition in which a larger proportion lie in a morenearly perpendicular relation to the cutting surface, assuming that thespaces between the grains are not unnecessarily filled with bondingmaterial. This statement also applies, although possibly in a lesserdegree, to abrasive grains which are not distinctly elongated, but havea greater number of pointed portions, or sharp points or edges, as thedullness of the surface will be greater and the cutting effect thereofwill be less if their sides lie flatwise to the surface than if theproportion of the pointed portions thereof which are pointed towards thesurface is substantially increased.

In other words the sharp or pointed ends of the grains have a muchgreater cutting effect than the sides thereof, as the sides presentpractically flat, or nearly fiat surfaces to the work, or points havingincluded angles which are relatively large, so that their action is morenearly a rubbing action which dislodges small particles, than adistinctly cutting or severing action. Moreover, an action which is moredistinctly a rubbing action has a much greater tendency to cause heatthan a, cutting action, on account of the fact that the friction is muchgreater in removing a certain amount of material than it would be ifremoved by an action which severs.

Where the abrasive grains are largely of elongated formation, and arepoured into the mold in the customary manner, the grains lie crisscrossand leave many unfilled spaces, resulting in a tool which lacks solidityand uniformity in its construction. Tests have shown and it is wellknown to manufacturers of abrasive tools, that the durability of suchtools, and the length of service which they will give depends to asubstantial extent on their weight per unit. of volume, or the densityor solidity thereof. In consequence it has been the practice to subjectthe elongated. grains tofurther treatment to reduce them to a nearlycubical or polyhedral form, so that the solidity of the tool would beincreased and each grain would present acorrespondingly large number ofsharp points, one of which would be likely to form a part of the workingface of the tool. produce cubical or polyhedral grains, increases Thisfurther treatment necessary to pared with the efliciency of devices ofthis character which are made by the methods now generally employed.

Further objects of my invention are to produce an abrasive tool whichmay be formed largely, or wholly of abrasive grains which are ofelongated formation, but which will be practically as solid, or freefrom voids as when formed from grains of the cubical or polyhedral type,so that the less expensive forms of abrasives may be employed, and, atthe same time a tool may be produced which will have increaseddurability, effective clearance at the cutting points, and an increasednumber of cutting points in the working face, so that the efficiencythereof will be substantially increased, as compared with tools formedfrom grains of the cubical or polyhedral ype.

I accomplish these objects by producing an abrading device which isprincipally composed of abrasive grains of elongated, orunequi-dimensional formation, so that one dimension is substantiallylonger than the others, and by arranging said grains so that they mainlylie side by side and are packed closely together, with their longer'dimensions extending in approximately perpendicular relation to theworking face, or in radial relation thereto when the tool is of thewheel type and has a circular face, said grains being securely bonded inthese positions, so that their ends will be presented to the work andthey will have deep settings which will prevent them from beingdislodged in use.

Inasmuch as it would not be practicable to arrange the grains in themanner above indicated separately by manual means, I have devised apractical and effective process of making such abrasive articles,whereby a relatively large proportion of the abrasive grains will bebonded in approximately the positions above indicated in relation to thework-engaging face of the particular abrading device which is to beproduced. This process, as described in said original application,primarily consists in showering, or otherwise gradually delivering theabrasive material to the mold, receptacle or other receiving means forthe abrasive, before final bonding, and while in a freely granularstate, and simultaneously subjecting the same to magnetic action, sothat the grains will become polarized and turned to point, or to havesome tapering portion thereof point in the direction of the lines offorce of the electric field, and by arranging the poles in such relationto the abrading surface to be formed that the above described resultwill be accomplished. Also, as magnetic action is to be employed, and asall, or nearly all abrasives which are likely to be employed arenon-magnetic, as a preliminary step in the process, and preferably inconnection with the operation of mixing the bond therewith, I providethe grains of abrasive with a coating of magnetic substance which will,in effect, make them sufliciently susceptible to magnetic influence toaccomplish the result desired, as by mixing very fine steel dust withthe abrasive grains and an adhesive of suflicient strength to hold thesteel particles on the surfaces thereof.

For a more complete description of the invention and of the means bywhich it may be perducing the abrasive tools which are the subject ofthis application, are specifically described in my said priorapplication, and will be only briefly .outlined herein. a

As all abrasive grains of the character above referred to arenon-magnetic and, as it is an essential, to the process which I employthat they be made susceptible to magnetic influence, a preliminary stepin said process consists in coating the grains with a suitable adhesiveand then mixing them with iron dust so that the iron dust will becomeadhesively connected thereto. That is, the grains will be partly, orwholly ferrous coated. These grains are then mixed with a suitablebonding material, and then are gradually showered into a mold of theshape of the tool to be formed, while they are, at the same time,subjected to the influence of a magnetic flux by means of an electromagnet, the poles of which are so arranged that the lines of forcethereof extend approximately at right angles to the working face of thetool to be formed, so that, as the grains fall into the mold the ferrouscoating on the grains will become polarized. As a result the ends of thegrains of elongated formation will have opposite polarities, and therewill be a strong tendency to cause the positively magnetized end of eachgrain to turn towards the negative pole of the magnet, and vice versa,or to turn the elongated grains in the direction of the lines of forceof the magnet.

In practice the poles of the electro-magnet are so arranged withrelation to a mold of the desired shape that the lines of forcetherebetween extend approximately in perpendicular relation to theworking face of the tool to be produced, so that when elongated grainsthus prepared, are showered into the mold, the electrical flux will tendto turn them into positions in which their longer dimensions extendtowards the side of the mold which forms the face of the tool. Inpractice the positioning of the grains take place while they are fallinginto the mold and after they come to rest therein, the positioning afterthey are supported in the mold being assisted by an automatic tapping orjarring action on the mold, which tends to dislodge incorrectlypositioned grains, so that they may be repositioned by the magneticattraction.

As the grains are mixed with a suitable bonding material before they areshowered into the mold, when the mold has been filled, as abovedescribed, it may then be subjected to the usual compressing and bakingprocess, so that the grains, as thus positioned, will be permanentlyset.

Referring now to the drawing, Figs. 1 and 2 indicate an abrasive tool aof the ordinary wheel or annular type, having flat, parallel sides and acylindrical working face a, and which is composed mainly of elongatedgrains, as b, which are covered partly or wholly with a thin coating cof ferrous material, as indicated on a greatly enlarged scale in Fig. 5.In this instance the grains 1) will be mainly arranged, throughout theentire mass, in approximately radial relation to the peripheral face ofthe wheel, and fiatwise 5 to its sides, as indicated in Fig. 1, so thatthe working face of the tool will be principally formed by the ends ofthese grains, as indicated in Fig. 2.

In Fig. 3, an abrasive tool d of another annular type is indicated whichhas a fiat working face e at each side. In this instance the grains arearranged fiatwise to the periphery and perpendicularly to the sides,orfaces e.

In Fig. 4i a tool I of the block type is shown, having a working face 9at one edge. In this instance the grains are mainly so arranged thattheir longer dimensions extend in approximately perpendicular relationto the face g.

It will be understood that, in practice, all of the grains will not beof elongated formation, but, as practically none of them will be ofspherical formation, they will at least be unequidimensional and thetendency of the electric flux will be to cause the more pointed portionsto become polarized oppositely to other portions, so that the action ofthe flux will be to tend to turn the grains so that their pointed endswill point .towards one pole or the other of the magnet.

As a result, comparatively few of the grains will be positioned in thetool, so that their sides will be presented to the work, but they willmainly be positioned so that their more pointed portions will bepresented thereto, or will form the work engaging face, and thiscondition will continue as the tool is worn down by use.

it will be understood that the various forms of tools shown are merelyillustrative and that the principles involved may be applied to otherforms of tools, although so far as I am aware, the most advantageousform is that of the ordinary wheel type shown in Fig. l, with which themost sub stantial increase in efficiency has been secured, as comparedwith similar types of tools in which the grains are arranged as theyhappen to fall into the mold.

An abrasive tool constructed principally or practically wholly ofelongated abrasive grains,

ged as above described, is particularly advantageous over similar tools,whether formed from the elongated, cubical, or' polyhedral type ofgrains, in which the grains are arranged as they happen to fall into themold, for several reasonsz-A tool constructed according to my inventionis heavier, more compact, or solid, and contains a substantially greaterquantity of abrasive material for the space occupied, than a similartool in which the elongated grains are arranged as they happen to fallwhen poured into the mold, and closely approximates in weight andsolidity to tools formed from abrasive grains which are practicallyequi-dimensional, or cubical, or of the polyhedral type.

The cutting efl'ect of a tool formed of abrasive grains of a certaingrit size is dependent on the number of cutting points per unit of areaof the working face of the tool, and a tool formed of elongated grainsarranged according to my invention presents a much greater number ofcutting points per unit of area, and therefore has a muchgreater cuttingeffect, than a tool formed of similar grains, but arranged as theyhappen.

but of relatively smaller grit size, and while the cutting points willthus be increased, the clearance spaces between the points will becorrespondingly reduced, resulting in a substantial reduction in thespeed at which the tool will cut, but, where the elongated grains areemployed and are arranged according to my invention, the desiredincrease in the number of cutting points is secured without decreasingthe grit size and without materially decreasing the clearance spacesbetween the cutting points, so that the speed at which the tool will cutwill be increased, and the tendency to generate heat when cutting willbe reduced. Also, with a tool formed from the practicallyequi-dimensional grains, as soon as the point of a grain which engagesthe work is worn or broken away, the entire grain is likely to bedislodged, while with the elongated grains arranged approximatelyperpendicularly to the working face, the ends of the grains aregradually broken or worn ofi, but the sharpness remains practically thesame, so that the entire grain will usually be removed in smallparticles and will not be dislodged, as each grain has a long, deepsetting and is bound in between the grains next adjacent thereto.

Abrasives which are most commonly used are of two general types,viz.-crystalline aluminum oxide and silicon carbide. The first of thesetypes is largely employed in grinding steel and steel alloys, as it hasgreater toughness than the second, which is too brittle and fragile foruse on steel. Some types of aluminum oxide are too tough for use onhardened steel, as the points become dulled, so that they stop cuttingand merely rub or abrade, causing heat and tending to discolor anddistort the steel on which the tool is operated. To adapt such abrasivesfor different kinds of work,-abrasive manufacturers have produced grainsof different temper varying from tough to relatively fragile, the latterbeing used for grinding very hard steel, so that the points will shatterand constantly present newcutting points to the work. Cubical orequi-dimensional grains when employed in a grinding wheel become bluntand are torn from their settings much more quickly than the radiallyarranged elongated grains, for reasons already stated. Also the latterhave sharper points than the former, and the angle between the sidesforming the point is smaller than in the cubical grains, so that whenelongated grains are employed in the construction of a wheel, and thegrains are radially arranged therein, the pointed ends break off morereadily than the points of the cubical grains. Consequently, the toughertypes of aluminum oxide may be employed, if the grains are elongated andarranged radially, where they could not be employed if they werecubical, and the wheel thus produced is not only more efficient, butgrains of the tougher types are usually approximately 50% less expensivethan those of the fragile types, so that a considerable saving inmanufacturing cost may be made by employing tough elongated grains,instead of fragile cubical grains for certain kinds of work. Moreover,all types of cubical and polyhedral grains are much more expensive toproduce than the elongated grains, so that by employing elongated grainsin the construction of abrasive tools and arranging the grains side byside in approximately perpendicular relation to the working face of thetool, I am enabled to produce a tool at a reduced cost, as compared withtools formed from abrasive grains which are practicallyequi-dimensional, and which, in addition, compares favorably with suchtools as to weight, durability and cutting points per unit of area andis substantially more efficient.

While the foregoing specification is largely directed to the advantagessecured by an arrangement of the grains approximately perpendicularly tothe abrading face of the tool. I have ascertained by experiment that asthe surface speed of an abrasive wheel made according to my invention isincreased above an approximate point of from 5,000 to 7,000 surface feetper minute, there is an increased tendency to cause the sharp ends ofgrains arranged perpendicularly to the abrading face to become shatteredby the increased force of impact due to the increased speeds, therebyindicating that at surface speeds in excess of that above noted thethicker portions of the grains were more effective than the thinnerportions, as the tendency to shatter was less. This led to theconclusion, which was verified by experiment, that, at surface speeds offrom 7,000 to 16,000 feet per minute, it was more advantageous to use aface in which the elongated grains were arranged parallel to, andtransversely of the abrading face, than to have them arrangedperpendicularly thereto, as, for example, the side face of the annulusshown in Fig. 1 of the drawing. and the peripheral face of that shown inFig. 3 of the drawing. In either of these instances the grains extendtransversely of the direction in which the face moves, and, while theadvantage of the deep setting of the grains secured by the perpendiculararrangement is lost, the tendency to shatter at high speeds is greatlyreduced. and a net increase in efiiciency is secured, particularly inthat the advantages of increased speed of cutting due to increasedsurface speed are secured without too rapid deterioration of the wheel.

I claim:

1. An abrasive tool composed of a rigid, bonded mass of abrasive grains,a substantial portion of which are of elongated formation and are mainlypositioned throughout the mass with their longer dimensions extendingtoward the working face of the tool at a similar angle, so that one endof each of said grains may terminate in said face either initially, orsubsequently from use, thereby to provide a maximum number of pointseflective for attritive action per unit of area of said face, and tosecure a maximum density of the grains per cubical unit of the tool anda maximum depth of setting of the grains. 1

2. An abrading tool composed of a rigid bonded mass of abrasive grains,a substantial portion of which are of elongated formation and are mainlypositioned side by side and end to end throughout the mass with theirlonger dimensions extending in approximately corresponding relation tothe working face of the tool.

3. An abrading tool having a circular, peripheral working face andcomposed of a rigid, bonded mass of abrasive grains, a substantialportion of which are of elongated formation and are mainly arranged withtheir longer dimensions extending approximately radially with relationto the center of said face.

4. An annular abrading tool having fiat sides and a cylindrical,peripheral working face and composed of a rigid, bonded mass of abrasivegrains, a substantial portion of which are of elongated formation andare mainly arranged throughout the mass in fiatwise relation to 'saidsides and in radial relation to said face.

5. An abrading tool composed of a rigid, bonded mass of ferrous coated,non-magnetic abrasive grains, a substantial portion of which are ofelongated formation, and are mainly arranged throughout the mass withtheir longer dimensions extending in approximately corresponding relation to the working face of the tool.

6. An abrasive tool composed of a rigid, bonded mass of abrasive grains,a substantial portion of which are of elongated formation, said toolhaving two faces disposed approximately at right angles to each other,and said elongated grains being mainly positioned so that they extendapproximately perpendicularly to one, an parallel to the other of saidfaces.

7. A rotary abrasive tool composed of a rigid, bonded mass of abrasivegrains, a substantial portion of which are of elongated formation, saidtool having a circular peripheral face and a side face, and saidelongated grains being mainly positioned so that they extendapproximately perpendicularly to one of said faces and transversely ofthe other of said faces with relation to the direction of movementthereof when the tool is rotated.

8. A rotary abrasive tool composed of a rigid, bonded massof abrasivegrains, a substantial portion of which are of elongated formation, saidtool having a cylindrical peripheral face, and a fiat side face, andsaid elongated grains being mainly positioned so that they extendapproxi mately perpendicularly to one of said faces and transversely ofthe other of said faces with relation to the direction of movementthereof when the tool is rotated.

9. A rotary abrasive tool composed of a rigid, bonded mass of abrasivegrains, a substantial portion of which are of elongated formation, saidtool having a cylindrical peripheral face and two flat side faces, andsaid elongated grainsbeing main 1y positioned so that they extendapproximately perpendicularly to said side faces and parallel to saidcylindrical face.

10. A rotary abrasive tool composed of a rigid, bonded mass of abrasivegrains, a substantial por-- tion of which are of elongated formation,said tool having a cylindrical peripheral face and parallel side faces,and said elongated grains being mainly positioned so that they extendapproximately perpendicularly to said side faces and parallel to saidcylindrical face.

. ORELLO S. BUCKNER.

